Display devices such as a touch panel including an input function in addition to a display function are widely used.
For example, patent document 1 discloses a liquid crystal display device that includes a liquid crystal display panel, imaging units each including an imaging optical system, detection light sources for emitting detection light with a wavelength in the infrared region along a viewer side of the liquid crystal display panel, and a backlight unit. The backlight unit includes light sources and an optical layer and is disposed such that a space is formed between the backlight unit and the liquid crystal display panel.
With the disclosed liquid crystal display device, display images are displayed on the liquid crystal display panel using the backlight unit, and images indicating touched positions in an input operation are obtained using the detection light sources and the imaging units. The detection light sources are arranged along the edges of a display area of the liquid crystal display panel so as to surround the display area. The imaging units are disposed inside of the backlight unit. Each of the imaging units receives the detection light that passes through the liquid crystal display panel and the imaging optical system from the viewer side and thereby obtains an image of the viewer side of the liquid crystal display panel. Also, fluorescent parts that transmit the detection light are provided in areas of the optical layer corresponding to the optical paths of the detection light entering the imaging units. The fluorescent parts absorb excitation light and emit visible light. This configuration makes it possible to prevent the imaging units from being viewed from the outside and to display high-quality images.    [Patent document 1] Japanese Laid-Open Patent Publication No. 2007-187753